Background: Heat stress as a major problem that strikes a lot of people, especially outdoor workers, throughout the world. Many parts of Iran have arid and semi-arid climates, in which high air temperature and radiant temperature, along with usually low humidity, cause hazardous conditions for outdoor workers in hot months. Therefore, in order to take every preventive measure to protect exposed workers against heat related disorders, it is indispensable to select an appropriate index that accurately relates environmental parameters to physiological responses. Objectives: This investigation aimed at investigating two heat stress and strain indices of wet bulb globe temperature-WBGT-and sweat rate, respectively, in order to examine their consistencies in arid and semi-arid climates of Iran. Methods: A total of 272 outdoor workers from different jobs were randomly selected and their sweat rate was calculated via a defined protocol three times a day. Simultaneously, environmental parameters, as well as WBGT index, were recorded for each working station. This study was performed during spring and summer. Results: The obtained results based on Kappa value showed a weak agreement between two standard indices. In addition, evaluation of outdoor workers using WBGT compared to sweat rate was accompanied by an overestimation. Moreover, based on mean and standard amounts of sweat rate, there were no cases exceeding the presented reference value regarding sweat rate at any time of the study. Conclusions: It seems that sweat rate standard level at a shift work may need some modifications related to the real condition of work in arid and semi-arid climates of Iran. In addition, judgment based on monitoring sweat rate alone, as a physiological response to heat in these climates, can be probably accompanied by underestimation